The present disclosure relates generally to devices that are inserted into the inner space of tubular members, and in particular to devices that have improved steerability features as a way to improve insertion into and movement within such members.
In general, there are numerous circumstances where a thin, elongate device must be inserted into a lengthy, narrow and often curved or branched tubular member in order to effect navigation and related repair, insertion or other complex activities associated with the device. With particular regard to minimally-invasive medical procedures, there is a need for flexible and steerable guide wires (also referred to herein as guide wire assemblies), stylets, catheters and related devices that generally have to be maneuvered through tortuous body lumens through one or more of pushing, pulling and tangential rotation, and more particularly do so by transferring such movements initiated at the proximal end of the device as accurately as possible to the distal end. While conventional guide wire assemblies with a steerable tip are known in the art as a way to achieve some degree of maneuverability, all have some form of drawback.
For example, some steerable devices have a shapeable tip at the distal end that can be bent to a desired angle before insertion. While the angle enables the operator to maneuver the device into side arteries or related branches in a body lumen, its relatively fixed nature means that once inserted, the tip angle cannot be changed, thereby limiting its subsequent mobility. To overcome the problems associated with such a fixed configuration, other devices have been developed to provide for a measure of remotely controlled steerability, such as by hand manipulation and related user actuation at the proximal end of the device. In one such example as shown by U.S. Pat. No. 6,599,254, the operator pulls a tension wire relative to the guide wire, so that the tip will bend in an amount that varies with the pulling force. In another example, U.S. Pat. No. 5,741,429 uses a hollow guide wire with a series of slots made in the tubular member wall at the place where more flexibility is desired. Relatedly, US Patent Application Publication 2003/0069522 shows that numerous pairs of slots are cut into the body to make it more flexible in bending while maintaining adequate torsional stiffness, while US Patent Application Publication 2004/0059257 shows numerous radial slots—all with the same cut depth—formed near the tip distal end, with the distance between the slits increasing farther away from the distal tip. In yet another example, U.S. Pat. No. 6,776,765 varies the depth of the slots over the length, with the deepest slots near the distal end, while keeping the axial distance between the slots identical, possibly in an attempt to vary the rigidity of the remaining tubular member material with slot depth. In still another example, U.S. Pat. No. 6,623,448 shows a device with an alternating pattern of opposing slots defined by a small linear offset; while such a configuration provides enhanced flexibility upon bending, the steerability is compromised, while manufacturing costs tend to be high. More significantly, fracture of the fragile wall near any slot causes complete failure of the device.
Helical slots have been proposed in an attempt to promote flexibility; however, it is difficult to achieve a reliable, repeatable one-to-one correspondence between the initiated rotation at the proximal end and the responsive rotation at the distal end. By way of example, U.S. Pat. No. 6,755,794 shows a single helical cut formed in the tubular member. The helix has an invariable pitch, and upon pulling the control wire, the gaps in the outer sheath all close at the same time, which in turn requires the device to remain straight regardless of whether the gaps are opened or closed. Such construction means that the only thing be varied is the rigidity of the device, so while a conventional helical cut can provide the selective flexibility needed to provide ample degrees of steerability, it has proven to be a vexing problem to use such cuts to keep a good reliable one to one rotational movement between proximal and distal ends.
In addition to steerability concerns, manufacturability issues must be addressed, especially where the device is meant for endoluminal use. In particular, as can be seen from the foregoing examples, normally laser cutting or similar techniques are used to form a pattern of slots into the wall of a tubular member. Such techniques (which often result in localized heating during the cutting process) tend to weaken the remaining material around the slot. This problem manifests itself during bending operations where elevated stress tends to be concentrated in a very localized region, leading to an increased risk of breakage in such region. The present Applicant believes that there is not enough remaining unharmed base material to absorb these stresses while the device is introduced and maneuvered into a tortuous path such as a body lumen. To overcome this elevated local stress problem, other approaches, such as that of U.S. Pat. No. 5,931,830 have been developed, where the member is produced by forming a strip of material into an elongate helical coil. Additional locks are used to improve the torsional stability, and while such an approach helps avoid or reduce the stress problems associated with traditional slot formation, the high costs render such approaches prohibitive, as does the inability to simultaneously control bending along with the increased torsional stability.